1. Field of the Invention
The invention pertains to rotary joints supplying steam to rotating heat transfer drums using stationary syphons for condensate removal.
2. Description of the Related Art
Rotating heat transfer drums such as of the type used in paper, corrugated paper and cardboard manufacture usually employ steam to heat the drum and a rotary joint located at the end of a hollow drum journal is used to introduce the steam into the drum interior. As the steam condenses within the drum, the condensate is removed through a rotary joint, usually the same joint which introduced the steam, and it is common for rotary joints to include both steam inlet ports and condensate exit ports.
Syphon systems for removing condensate from rotating heat transfer drums are either of the "rotating" type where the conduit pickup occurs at a shoe contacting the drum interior and wherein the syphon structure within the drum rotates with the drum, or the syphon system may be of the "stationary" type wherein the condensate pickup apparatus extends into the drum interior, but does not rotate with the drum, and includes a condensate pickup port disposed adjacent the drum shell interior.
Whether a heat transfer drum employs a rotating syphon system or a stationary syphon system depends on various factors including cost, size of the drum, rate of drum rotation, material to be heated and other factors. Both types are well known in the dryer drum art.
The installation of a rotating syphon system usually requires that considerable installation work occurs within the drum interior. This is not a problem with large size dryer drums which have access openings located in the drum ends. However, with smaller sizes of drums, it is usually necessary to employ a stationary syphon system whereby the syphon structure may be inserted through the hollow drum journal, and once inserted, the syphon pipe portion of the syphon system is moved to an operating location within the drum adjacent the drum shell inner surface for removing condensate therefrom. Samples of such stationary syphon systems are shown in U.S. Pat. Nos. 2,542,287; 2,732,228; 3,265,411; 4,590,688 and 5,533,569.
It has long been recognized that the puddle of condensate which accumulates in the lower region of the dryer drum creates problems. This condensate accumulation "tumbles" within the drum as it rotates requiring excessive power, and deleteriously affects the heat transfer from the steam within the drum to the drum shell. In rapidly rotating larger drums, this condensate forms a film throughout the drum periphery, and can be effectively removed by a rotating syphon system wherein the condensate film is removed and maintained of minimum thickness. With a stationary syphon system, condensate is only removed at the lower region of the drum, and the condensate accumulation in the lower region of the drum will exist unless the drum rate of rotation is high enough to cause the condensate to "film" about the drum periphery.
Because of the "insulation" effect that condensate accumulation has on heat transfer from the steam to the drum, it is particularly important when manufacturing corrugated fluted paper and cardboard to be able to accurately maintain the temperature of the drum very closely as to accurately control the humidity content of the paper being dried by the drum. Heretofore, stationary syphon systems often fail to maintain the desired distance between the syphon pipe intake and the drum shell interior surface as to minimize the condensate accumulation and provide optimum uniform heat transfer characteristics and control to the drum. Prior stationary syphon systems required that the spacing of the syphon pipe inlet from the drum interior surface be determined by regulating the length of the syphon pipe, and due to manufacturing tolerances in drum manufacture, and because of variations in rotary joint installations, it is very common that a greater spacing exists between the syphon pipe pickup entrance and the drum shell than is desired, resulting in an excessive accumulation of condensate and uneven heating of the drum shell.